You can add existing files to the project by right clicking the project folder in the project tree of the Creator. The popup menu contains item "Add Existing Files". Add existing files A few recommendations:

(1) Keep all project files in some manageable structure. Do not allow project files scattered over your disk. Copy all existing files to subdirectories of your project directory.
(2) Patch the profile file yourself as little as possible and let the Creator to manage the profile file. Specify TEMPLATE, QT, TARGET, INCLUDEPATH, DEPENDPATH, LIBS. The rest can be done from the Creator: Add files, add existing files, remove files, rename files, resources, forms (a new .ui file -> add existing files).